This invention relates to a coil element, particularly to a tiptype coil element.
Recently, digital wrist watches equipped with an alarm device have been developed. Such an alarm device employs a piezo-electric alarm circuit comprising a small boosting coil. The inventors of this present application have proposed in Japanese patent application No. 53,925/80 (publication No. 150,807/81, laid open Nov. 21, 1981), corresponding to U.S. application Ser. No. 185,526 filed Sept. 9, 1980, and assigned to the same assignee as this present application, a boosting coil for such purpose which comprises a drum-shaped core, a pair of semicylindrical ferrite cores attached around the drum shaped core, and electrodes, i.e., terminals, formed by plating on the outer surfaces of the respective semicylindrical ferrite cores for connecting the boosting coil to a corresponding circuit. In such a boosting coil element, the inner surface of each semicylindrical ferrite core is required to be formed with high precision to make the radius of curvature of the inner surface of the semicylindrical ferrite core coincide with that of the outer surface of the drum-shaped core, so that the semicylindrical ferrite core fits to the outer surface of the drum-shaped core. Furthermore, such a booster core element has to be subjected to a plating process to provide the electrodes, which requires complex manufacturing processes.
This invention is directed to improving the above coil element. A coil element in accordance with the present invention comprises a drum-shaped ferrite core on which a coil is wound, magnetic members each made of a magnetic and electrically conductive metal and formed so as to fit to the outer surface of the drum-shaped ferrite core and spaced from each other so as to be electrically insulated from each other, and connection terminals forming a part of the magnetic members connected to the ends of the coil. Each magnetic member is generally of arcuate cross-sectional shape, and the radius of curvature of the arc of each magnetic member is slightly less than that of the drum-shaped ferrite core.
A preferred embodiment of the present invention is described below, with reference to the attached drawing.